Early detection of fires and flames is very important in the industrial and domestic environments. Domestic sensors tend to detect combustion bi-products which are, of course, produced after a fire has started, detection occurring once those by-products have reached the sensor—which can be some distance from the fire. Early detection of fires is essential in many environments where untold damage can occur very quickly and where there is a serious risk to safety. Flame detectors per se are known in the art and do provide early warning of the existence of fires, and such detectors are often located to monitor specific equipment, etc. where there is an increased risk of fire.
FIG. 2 (although it additionally shows aspects of the invention, it is here referred to so as to identify background information known to those skilled in the art and help set the scene) is an example of the approximate electromagnetic spectrum produced by burning petrol—line 20 represents the approximate relationship of energy vs wavelength. Line 20 may be sectioned into three approximate regions. A first region, identified with I, represents both the ultraviolet and visible regions of the spectrum; a second region, identified with II, represents the near-infrared and short-/mid-infrared, which includes a characteristic black body-type heat signature emitted by a flaming material; and the third region, identified by III, represents the mid-/long-infrared which includes the carbon dioxide (hereinafter CO2) peak at 4.3 microns. Whilst it is not intended to be bound by theory, when a material becomes hot, for example during combustion, the amount of radiation (blackbody-type radiation) increases, together with a corresponding movement of the wavelength towards the shorter wavelengths. Hereinafter, ultraviolet may be designated ‘UV’ and infrared may be designated ‘IR’.
A predominance of known flame detectors look for the signal produced by hot gases, like CO2 at 4.3 microns, as this is representative of the burning of many fuels. However, not all fuels contain carbon and, as such, when a fuel such as hydrogen burns, there is no CO2 peak produced. In that situation, those known detectors cannot detect the presence of a flame or fire, as the sensors used therein are entirely blind to other parts of the spectrum produced by a flaming material. Further, such detectors cannot distinguish between a flame producing CO2 and CO2 produced by, for example, an engine. Additionally, real-world fires typically produce a large amount of dirt, soot and smoke. The presence of smoke, soot and other particulates makes fires very challenging to detect, as the smoke created by a ‘dirty’ flame can block the tell-tale 4.3 micron signal. A further particular disadvantage of narrowband detectors aimed at the 4.3 micron peak is that, in a situation that the fuel is burning in a confined space, carbon monoxide might be created rather than CO2, which would lead to a reduced 4.3 micron peak. This can significantly affect the speed of detection. A further disadvantage of these detectors is that, as known by those skilled in the art, 4.3 micron light is blocked by regular glass and, therefore, expensive sapphire windows must be used. Additionally, the 4.3 micron peak can be readily blocked by contaminants, such as water vapour, dirt, ice and snow. Accordingly, such known detectors are often heated and must be cleaned to ensure their correct functioning, which increases the overall cost of the unit and the running cost of the unit and associated infrastructure.
It is, therefore, understood by the Applicant that directing a flame detector to only around the 4.3 micron peak has clear disadvantages. As such, a more rounded and useful flame detector could be produced by increasing the range of wavelengths detected, which has led to a phrase coined by the Applicant: BROADSPECTRUM™.
There are many infrared sensors which exist in the marketplace, each having different characteristics of performance and cost. Generally speaking, the wider the effective range of detection of the sensor, the more expensive the sensor. Therefore, with respect to narrowband detection, this is not so much of an issue as the spectral peaks which they are intended to detect are themselves narrow; however, it becomes more of an issue when one is trying to detect wider peaks or significantly more of the spectrum emitted by a flame.
Infrared sensors come in a variety of different types, each based on a different semi-conductor metal salt. Each sensor has a different response to temperature and its relative degradation over time. As a result, detectors that rely upon interplay of various different sensors will give variable detection with temperature change and their performance will change over time as the sensors degrade at different rates. As such long-term detection of the unit can be compromised.
Further, there are a number of manufacturers who supply a range of flame detectors, each having its own detection characteristics and associated cost. Many manufacturers seem to believe that the inclusion of a plethora of sensors within the same detector provides for better detection, and sometimes this is true; however, as the sensor becomes more advanced and more numerous, the associated cost of the unit increases.
As such, there exists in the marketplace a need for a powerful (in that it is not narrowband) flame detector which, although economically produced, does not compromise on the accuracy of detection. The present invention is aimed at providing early detection of flames and fires but without the associated significant expense of various sensors on the market.